Techniques are known for sealing joints when manufacturing packages. One example of such a known technique is ultrasonic sealing, where ultrasonic energy is applied to a hot-binding medium provided in the joint to seal it. According to another known technique, an adhesive is applied in the joint for sealing. If the joint is of such a kind that it comprises one conductive medium and one hot-binding medium, induction heat sealing can be used to seal the joint.
U.S. Pat. No. 5,889,263 discloses an apparatus for induction sealing of a packaging material comprising an aluminium foil layer. The apparatus comprises an inductor with two parallel conductors interconnected by two transverse conductors. The parallel conductors are disposed in an electrically insulated carrier portion. The transverse conductors are arranged in the upper surface of the inductor and coincide with the outer defining lines of a flat-laid tube of packaging material. The inductor is comprised in a sealing jaw, which is arranged to squeeze a double layer of the packaging material against a counter jaw. The parallel conductors are connected to a current source, whereby an induction current is generated in the aluminium foil layer. Heat is generated, and each of the conductors forms one seal of the packaging material. Between these two seals, the package material may be cut. Thus, by means of this apparatus, one seal of each of two packages can be formed at a time. The apparatus is limited for sealing joints between mutually united and compressed layers of the packaging material, i.e. for transverse sealing of a flat-laid tube of packaging material.
U.S. Pat. No. 6,079,185 discloses an induction sealing device for sealing a closure about an access area of a container. Either the closure or the container comprises a metal medium forming a continuous conductive area around the access area. A conductor is arranged to be provided around the access area, on the outside of the closure and the container. A flowing current in the conductor causes an induced current in the metal medium, which induced current follows the flowing current around the access area. Heat is generated, by means of which the closure is chemically bonded to the container along a joint.
The above mentioned induction sealing device is limited to cases where a continuous conductive area is provided along the entire joint to be sealed. If there should be a discontinuity present in the conductive area, the induced current would be prevented from following the flowing current around the complete access area, and instead would be spread into undesired areas. Such a spreading might cause damaging generation of heat in these undesired areas. Further, the generation of heat in the desired area might be insufficient, a bad sealing of the joint being the result.